Long-Term Bonding Performance of One-Bottle vs. Two-Bottle Bonding Agents to Lithium Disilicate Ceramics

The aim of this study was to compare the long-term bonding performance to lithium disilicate (LDS) ceramic between one-bottle and two-bottle bonding agents. Bonding performance was investigated under these LDS pretreatment conditions: with hydrofluoric acid (HF) only, without HF, with a two-bottle bonding agent (Tokuyama Universal Bond II) only. Shear bond strengths between LDS and nine resin cements (both self-adhesive and conventional adhesive types) were measured at three time periods: after one-day water storage (Base), and after 5000 and 20,000 thermocycles (TC 5k and TC 20k respectively). Difference in degradation between one- and two-bottle bonding agents containing the silane coupling agent was compared by high-performance liquid chromatography. With HF pretreatment, bond strengths were not significantly different among the three time periods for each resin cement. Without HF, ESTECEM II and Super-Bond Universal showed significantly higher values than others at TC 5k and TC 20k when treated with the recommended bonding agents, especially at TC 20k. Difference in degradation between one- and two-bottle bonding agents containing the silane coupling agent was compared by high-performance liquid chromatography (HPLC). For both cements, these values at TC 20k were also not significantly different from pretreatment with only Tokuyama Universal Bond II. For LDS, long-term bond durability could be maintained by pretreatment with Tokuyama Universal Bond II instead of the hazardous HF.


Introduction
As a dental restorative material, lithium disilicate (LDS) outshines traditional metals in many core features.Not only does it have comparable wear resistance, it possesses favorable properties lacking in many dental metals: teeth-mimicking aesthetics and good machinability.The widespread use of LDS is also fuelled by the popular CAD/CAM (computer-aided design and computer-aided manufacture) technology.CAD/CAM is gaining traction in restorative dentistry because it eliminates the reliance on techniquesensitive laboratory procedures and the need to ship restorations.In terms of chairside benefits, CAD/CAM provides a significant leap in patient's comfort [1][2][3][4][5][6][7][8][9][10][11][12][13][14].
Durable bond strength is critical to the longevity of dental restorations.It is noteworthy that LDS exhibits poor bonding with resin cements.Presently, LDS surfaces are pretreated with hydrofluoric acid (HF) to form micromechanical interlocking force to the end of securing long-term adhesiveness.HF is a weak acid that reacts with and dissolves glass (SiO 2 ).However, it is also a dangerous acid that can be easily absorbed into blood through the skin, leading to health hazards such as cardiac arrest [15,16].Since HF cannot be used intraorally, alternatives such as phosphoric acid, acidulated phosphate fluoride and Polymers 2024, 16, 2266 2 of 15 ammonium hydrogen fluoride have been used as substitutes.However, they fail to achieve HF's efficacy in bonding durability.
As mentioned above, phosphoric acid is a non-toxic substitute for HF intraorally.However, phosphoric acid could neither create adequate micromechanical retention nor remove silicon oil contamination.As for the effectiveness of phosphoric acid etching on bonding to glass-ceramics, contentious results have been reported.For LDS, bonding effectiveness is pivotally important because compared with other traditional ceramic materials, LDS pales in fracture toughness and defect tolerance.This means that LDS restorations are prone to fracture.Sandblasting is a repair system for intraoral all-ceramic fractures [17], but it risks injuring the surrounding soft tissues and spreading aluminium oxide particles over the operative area [18].
A new type of bonding system categorized as "universal" has been introduced.Universal bonding system is a one-step system that can be applied to enamel and dentin substrates in clinical situations.It can also be applied to bonded restorative materials such as zirconia, metal and silicate-based ceramics without surface pretreatment using a priming agent.This bonding system augurs well for LDS.LDS is a popular glass-ceramic material for single crowns-is compatible with adhesives, self-adhesives and conventional cements [7][8][9].The introduction of a new universal bonding system thus offers a simplified approach to enhance the bond strength between LDS and resin cements [8].
Many one-bottle bonding agents which contain silane coupling agent are marketed with a prominent emphasis on convenience.The most common silane coupling agent used in dentistry is γ-PTS (gamma-methacryloxy propyl trimethoxy silane) which is diluted in an ethanol-water solution.
To circumvent the deterioration in the adhesion-promoting efficacy of silane coupling agent, two-bottle bonding agents ¾ which separate unhydrolyzed silane from aqueous solution ¾ were introduced [5,6].
To obtain more information and insights on the long-term bonding performance of a palette of clinically applied resin cements, this study investigated the adhesive strengths of nine resin cements to LDS with and without HF pretreatment.These nine adhesive and self-adhesive resin cements were selected such that the bonding durability effects of silane coupling agent, one-and two-bottle bonding agents were investigated after one-day water storage (abbreviated as Base), and after 5000 and 20,000 thermocycles (abbreviated as TC 5k and TC 20k respectively).Difference in degradation between oneand two-bottle bonding agents containing the silane coupling agent was compared by high-performance liquid chromatography (HPLC).
The null hypotheses of this study were: (1) two-bottle bonding agent would provide durable bond strength to LDS without HF pretreatment; and (2) bond strength provided by one-bottle bonding agent to LDS would deteriorate over time due to long-term immersion in water, and (3) the usefulness of the HY treatment of Tokuyama Universal Bond II was also examined.

Resin Cements and Bonding Agents
Table 1 lists the details of the nine adhesive and self-adhesive resin cements selected for this study.As the focus of this study was to investigate the shear bond strength to LDS with respect to pretreating agent, distinction between two dual-cure resin cements in terms of conventional versus self-adhesive types was deliberately omitted.This range was thus selected to represent the major restorative products used by dentists and to provide a comprehensive, clinically relevant range of values for the parameters under investigation.1.In this study, LDS was also applied with pretreating agent for the selfadhesive type due to the research aims of this study; moreover, adhesion to tooth substrate is different from adhesion to LDS.A single operator (MI) performed all the mixing, handling and bonding procedures according to manufacturers' recommendations (Table 2).Ten specimens were prepared for each material for evaluation of their mechanical properties at each time period (after one day, and after TC 5k and TC 20k).For the resin cements, a visible light curing unit (New Light VL-II, GC, Tokyo, Japan; fiber optic tip diameter: 8 mm) was used to irradiate light-activated materials for 20 s.Using a radiometer (Demetron/Kerr, Danbury, CT, USA), light intensity was checked immediately before the application of each resin cement.During light curing, light intensity was maintained at 450 mW/cm 2 .Since the polymerization of Super-Bond Universal is in self-cure mode, all measurements were made only in self-cure mode.All procedures, except those for shear bond strength measurement, were performed in a thermo-hydrostatic room maintained at a temperature of 23 ± 0.5 • C and relative humidity of 50 ± 2%

Shear Bond Strength Measurement
A split Teflon mold with a cylindrical hole (diameter: 3.6 mm, height: 2 mm) was clamped to the prepared LDS surface in a mounting jig.The Teflon mold was filled with each resin cement using a syringe tip (Centrix C-R Syringe System, Centrix, CT, USA).Shear bond strength measurements were performed at three time periods: (i) after oneday storage in distilled water at 37 • C (Base); after (ii) 5000 and (iii) 20,000 thermocycles (thermal stress between 5 and 55 • C; 1 min dwell time), abbreviated as TC 5k and TC 20k respectively.
For each shear bond strength measurement, a shear force was applied using a universal testing machine (Autograph AG-X 20kN, Shimadzu, Kyoto, Japan) at a crosshead speed of 0.5 mm/min.The force was transmitted via a flat (blunt), 1-mm-thick shearing blade at a perpendicular direction to the load.Stress at failure was calculated and recorded as the shear bond strength.Failed specimens were examined under a light microscope at ×4 magnification (SMZ-10, Nikon, Tokyo, Japan) to determine the total number of adhesive failures [14].

High-Performance Liquid Chromatography Analysis
To compare the degradation between one-bottle and two-bottle bonding agents which contained the silane coupling agent.
High-performance liquid chromatography (HPLC) analysis was performed on Scotchbond Universal Plus Adhesive (one-bottle bonding agent) and Tokuyama Universal Bond II (two-bottle bonding agent).In this study, the adhesive of most interest is Tokuyama Universal Bond II, and Scotchbond Universal Plus adhesive, which is widely used worldwide, was used as a control.For these reasons, these two adhesives were used for the measurements.Both bonding agents were described to contain 3-(triethoxysilyl) propyl methacrylate (MPTES) on Safety Data Sheet (SDS).
Measured samples of Scotchbond Universal Plus Adhesive, Tokuyama Universal Bond II and MPTES were each diluted with acetonitrile (CH3CN) containing 0.005 wt.% naphthalene.An LC-20 AD pump (Shimadzu, Kyoto, Japan) was used to deliver the mobile phase to the analytical column at a flow rate of 1.0 mL/min.Chromatographic separation was achieved using a Umisil C18 analytical column (250 mm, 6 mm φ, 5 µm; GL Science, Tokyo, Japan) at 30 • C with CH3CN/H2O.Detection was achieved at a wavelength of 210 nm using an SPD-M20A UV-VIS detector (Shimadzu, Kyoto, Japan).Retention times and absorption wavelengths of HPLC chromatogram peak of MPTES for Scotchbond Universal Plus Adhesive and Tokuyama Universal Bond II were analyzed.

Statistical Analysis
Statistical analysis was performed using the software package, Statistical 9.1 (Statsoft, OK, USA).Analysis of variance (two-way ANOVA) with Tukey-HSD for post-hoc comparison was used to analyze the data obtained for shear bond strength to LDS (p < 0.05).Comparisons of the means for shear bond strength to LDS of each resin cement with regard to one-vs.two-bottle bonding agents were done by one-way ANOVA) with t-test (p < 0.05).Analyses were conducted using SPSS version 19 (Chicago, IL, USA).

With and without HF Pretreatment
Table 3 shows the shear bond strength data between LDS and the resin cements with and without HF pretreatment.For each resin cement, adhesive strengths of their HF-treated [HF (+)] specimens were not significantly different among the three time periods (Tables 3 and 4).Without HF [HF (−)], their adhesive strengths significantly differed over time and became almost zero at TC 20k (p = 0.05; Tables 3 and 4).However, HF (−) specimens of ESTECEM II and Super-Bond Universal showed approximately 20 MPa at TC 20k.   3 and 4) For both HF (+) and HF (−) specimens of each resin cement, highest value was yielded at the Base (one-day water storage) time period.
Overall, RelyX Universal Resin Cement showed the greatest values among the six conditions (three time periods, both HF (+) and HF (−) specimens).
With HF pretreatment, Variolink Esthetic DC showed the highest values at TC 5k and TC 20k.Without HF pretreatment, ESTECEM II and Super-Bond Universal showed the highest values at TC 5k and TC 20k.The disparate results shown in Table 3 were statistically classified into many groups (p < 0.05) in Table 4.  5) With HF pretreatment, the data were not statistically different within each time period among the resin cements (Table 5).TC 5k: after 5000 thermocycles, TC 20k: after 20,000 thermocycles.
Without HF pretreatment, ESTECEM II and Super-Bond Universal showed significantly better values than the other cements at all the three time periods.Conversely, PANAVIA SA Cement Universal showed significantly lower values than the other cements at all the three time periods.

Statistical Comparison between HF (+) and HF (−) Specimens of Each Resin Cement
for Each Time Period (Tables 3 and 6) Table 6 shows a total of 27 comparisons (multiple of three time periods for each of the nine resin cements).Each comparison entails a pair of statistical analyses between HF (+) and HF (-) specimens at each time period.TC 20k: after 20,000 thermocycles.

Statistical Comparison between Two Pretreating Agents at Each Time Period (Table 10)
All conditions showed significantly superior results when treated with Tokuyama Universal Bond II (except Variolink Esthetic DC at Base and Super-Bond Universal at TC 20k).

Chemical Analysis of MPTES by HPLC
HPLC results for Tokuyama Universal Bond II, Scotchbond Universal Plus Adhesive and MPTES are shown in Figures 1 and 2. For Tokuyama Universal Bond II, a peak was identified at the same retention time (67.2 min) as MPTES.Figure 3 shows the absorption wavelength of the peak at retention time 67.2 min for Tokuyama Universal Bond II, whereas that of MPTES is shown in Figure 4.The corresponding peaks showed similar absorption wavelengths.Based on these results, it was confirmed that MPTES was contained in the Tokuyama Universal Bond II product as stated in the SDS.

Chemical Analysis of MPTES by HPLC
HPLC results for Tokuyama Universal Bond II, Scotchbond Universal Plus Adhesiv and MPTES are shown in Figures 1 and 2. For Tokuyama Universal Bond II, a peak wa identified at the same retention time (67.2 min) as MPTES.Figure 3 shows the absorption wavelength of the peak at retention time 67.2 min for Tokuyama Universal Bond II whereas that of MPTES is shown in Figure 4.The corresponding peaks showed simila absorption wavelengths.Based on these results, it was confirmed that MPTES was con tained in the Tokuyama Universal Bond II product as stated in the SDS.TC 20k: after 20,000 thermocycles, S: Significant difference (p < 0.05), NS: Not significant differenc (p > 0.05).

Chemical Analysis of MPTES by HPLC
HPLC results for Tokuyama Universal Bond II, Scotchbond Universal Plus Adhesiv and MPTES are shown in Figures 1 and 2. For Tokuyama Universal Bond II, a peak wa identified at the same retention time (67.2 min) as MPTES.Figure 3 shows the absorption wavelength of the peak at retention time 67.2 min for Tokuyama Universal Bond II whereas that of MPTES is shown in Figure 4.The corresponding peaks showed simila absorption wavelengths.Based on these results, it was confirmed that MPTES was con tained in the Tokuyama Universal Bond II product as stated in the SDS.

Discussion
This study investigated the long-term bonding performance of different pretreatmen methods by comparing shear bond strengths between nine clinically applied resin ce ments and LDS over three time periods: after one-day water storage (Base), TC 5k and TC 20k.The pretreatment methods investigated were: (i) with or without HF; and (ii) one bottle versus two-bottle bonding agents which contained silane coupling agent.
In this study, thermocycling tests of 20,000 thermocycles were carried out becaus they aptly represent the conditions in the oral cavity [14].According to the literature [23] provisional estimate of approximately 10,000 cycles per year was suggested.Therefore we consider the thermocycles 20,000 times to be a two year in vivo condition.

HF (+) versus HF (−)
When LDS was pretreated with HF, porous concavo-convex surface and micro retentions were produced due to HF selectively dissolving the glassy matrix.Roughness is a vital surface property of restorative materials, influencing the substances' abrasiveness

Discussion
This study investigated the long-term bonding performance of different pretreatmen methods by comparing shear bond strengths between nine clinically applied resin ce ments and LDS over three time periods: after one-day water storage (Base), TC 5k and TC 20k.The pretreatment methods investigated were: (i) with or without HF; and (ii) one bottle versus two-bottle bonding agents which contained silane coupling agent.
In this study, thermocycling tests of 20,000 thermocycles were carried out becaus they aptly represent the conditions in the oral cavity [14].According to the literature [23] provisional estimate of approximately 10,000 cycles per year was suggested.Therefore we consider the thermocycles 20,000 times to be a two year in vivo condition.

HF (+) versus HF (−)
When LDS was pretreated with HF, porous concavo-convex surface and micro retentions were produced due to HF selectively dissolving the glassy matrix.Roughness is a vital surface property of restorative materials, influencing the substances' abrasiveness

Discussion
This study investigated the long-term bonding performance of different pretreatment methods by comparing shear bond strengths between nine clinically applied resin cements and LDS over three time periods: after one-day water storage (Base), TC 5k and TC 20k.The pretreatment methods investigated were: (i) with or without HF; and (ii) one-bottle versus two-bottle bonding agents which contained silane coupling agent.
In this study, thermocycling tests of 20,000 thermocycles were carried out because they aptly represent the conditions in the oral cavity [14].According to the literature [23], provisional estimate of approximately 10,000 cycles per year was suggested.Therefore, we consider the thermocycles 20,000 times to be a two year in vivo condition.

HF (+) versus HF (−)
When LDS was pretreated with HF, porous concavo-convex surface and micro retentions were produced due to HF selectively dissolving the glassy matrix.Roughness is a vital surface property of restorative materials, influencing the substances' abrasiveness and mechanical retention despite stresses from the external environment.Surface roughness is not the only determinant of material adhesion; it is also influenced by other characteristics, such as porosity, residual microstructural tension, composition, and mass defects [6].
HF pretreatment created a rough surface which provided micromechanical retention for the resin cement.It also produced microporosity which helped to facilitate resin penetration and significantly improve bond strength [3,[17][18][19].Microporosity also resulted in appreciably larger surface area for interaction with silane to increase wettability.
Increase in wettability led to increase in surface energy.Therefore, HF improved micromechanical interlocking by increasing surface roughness, and it also enhanced chemical bonding with resin cement due to increase in surface energy on silane-treated LDS.Results of this study showed that HF pretreatment followed by silane application resulted in the highest bond strength values.Moreover, the most favourable surface treatment for LDS was pretreatment with HF followed by application of silane coupling agent in a two-bottle adhesive.
Based on the above reasons and the results obtained in this study, it is suggested that HF (+) protocol produced more durable bonding than HF (−) protocol.

One-Bottle versus Two-Bottle
Silane coupling agent application is known to improve the bond strength to LDS and silica-based ceramics.It was reported that chemical bonds between LDS and resin composite luting materials could be achieved by the silanol group of silane molecules reacting with silica on the ceramic surface.
In this study, Tokuyama Universal Bond II and M&C Primer (which were two-bottle bonding agents) provided significantly better long-term durability (TC 20k) to LDS than onebottle bonding agents.In two-bottle pretreating agents, hydrolysis of the silane coupling agent could occur only when the two components were mixed during use, resulting in the formation of silanol groups (Figure 5).Consequently, the number of silanol groups that could condense and react with LDS (Figure 5) was higher than that yielded by one-bottle pretreating agents.In other words, two-bottle bonding agents provided a higher number of chemical bonds to LDS than one-bottle bonding agents, thereby averting a significant decrease in their bond strengths during durability tests.
Polymers 2024, 16, x 14 of 17 and mechanical retention despite stresses from the external environment.Surface roughness is not the only determinant of material adhesion; it is also influenced by other characteristics, such as porosity, residual microstructural tension, composition, and mass defects [6].HF pretreatment created a rough surface which provided micromechanical retention for the resin cement.It also produced microporosity which helped to facilitate resin penetration and significantly improve bond strength [3,[17][18][19].Microporosity also resulted in appreciably larger surface area for interaction with silane to increase wettability.
Increase in wettability led to increase in surface energy.Therefore, HF improved micromechanical interlocking by increasing surface roughness, and it also enhanced chemical bonding with resin cement due to increase in surface energy on silane-treated LDS.Results of this study showed that HF pretreatment followed by silane application resulted in the highest bond strength values.Moreover, the most favourable surface treatment for LDS was pretreatment with HF followed by application of silane coupling agent in a twobottle adhesive.
Based on the above reasons and the results obtained in this study, it is suggested that HF (+) protocol produced more durable bonding than HF (−) protocol.

One-Bottle versus Two-Bottle
Silane coupling agent application is known to improve the bond strength to LDS and silica-based ceramics.It was reported that chemical bonds between LDS and resin composite luting materials could be achieved by the silanol group of silane molecules reacting with silica on the ceramic surface.
In this study, Tokuyama Universal Bond II and M&C Primer (which were two-bottle bonding agents) provided significantly better long-term durability (TC 20k) to LDS than one-bottle bonding agents.In two-bottle pretreating agents, hydrolysis of the silane coupling agent could occur only when the two components were mixed during use, resulting in the formation of silanol groups (Figure 5).Consequently, the number of silanol groups that could condense and react with LDS (Figure 5) was higher than that yielded by onebottle pretreating agents.In other words, two-bottle bonding agents provided a higher number of chemical bonds to LDS than one-bottle bonding agents, thereby averting a significant decrease in their bond strengths during durability tests.Although all LDS surfaces in this study were treated with a silane coupling agent, bond strength results were observed to be material-and time-dependent [16,18,19].Without HF pretreatment, bond strength results were close to zero at TC 20k, except when pretreated with two-bottle bonding agents.Therefore, results of this study supported the hypothesis that two-bottle bonding agent could provide durable bond strength to LDS without HF pretreatment.

Analysis of MPTES by HPLC
After production, MPTES in Scotchbond Universal Plus Adhesive is expected to decompose because the presence of MPTES, phosphate monomer and water in the same bottle would promote hydrolysis and dehydration condensation of MPTES.
As shown in Table 2, Scotchbond Universal Plus Adhesive contained phosphate monomer, water and MPTES in one bottle.As shown in Figure 5, coexistence of these three Although all LDS surfaces in this study were treated with a silane coupling agent, bond strength results were observed to be material-and time-dependent [16,18,19].Without HF pretreatment, bond strength results were close to zero at TC 20k, except when pretreated with two-bottle bonding agents.Therefore, results of this study supported the hypothesis that two-bottle bonding agent could provide durable bond strength to LDS without HF pretreatment.

Analysis of MPTES by HPLC
After production, MPTES in Scotchbond Universal Plus Adhesive is expected to decompose because the presence of MPTES, phosphate monomer and water in the same bottle would promote hydrolysis and dehydration condensation of MPTES.
As shown in Table 2, Scotchbond Universal Plus Adhesive contained phosphate monomer, water and MPTES in one bottle.As shown in Figure 5, coexistence of these three components resulted in the hydrolysis of MPTES.Silanol groups were generated, and dehydration condensation between silanol groups led to the oligomerisation of MPTES.With all these reactions occurring in the single bottle, it is suggested that MPTES was thus depleted from the composition, although this was not confirmed by HPLC in this study.
On the other hand, Tokuyama Universal Bond II contained MPTES and water in Liquid B and phosphate monomer in Liquid A (Table 2).As MPTES and water were separated from the phosphate monomer, the hydrolysis of MPTES was unlikely to occur.Hence, the presence of undecomposed MPTES was clearly confirmed by HPLC in this study.
Adhesion to LDS is achieved by condensation reactions between silanol groups in silane coupling agent and silanol groups on LDS surface to form chemical bonds.
In one-bottle pretreating agents, hydrolysis and dehydration condensation of the silane coupling agent occurred within the product, thereby reducing the number of silanol groups in the silane coupling agent.Consequently, the number of silanol groups that could condense and react with LDS was reduced.Chemical bonds formed by the silane coupling agent to LDS became inadequate, such that adhesive strength deteriorated and decreased during durability tests.
In two-bottle pretreating agents, hydrolysis of the silane coupling agent within the product was unlikely to occur before the two bottles were mixed.When silanol groups were formed by hydrolysis of the silane coupling agent during use (that is, when the two bottles were mixed), the number of silanol groups that could condense and react with LDS was higher than that rendered by one-bottle pretreating agents.With adequate chemical bonding to LDS in this case, adhesive strength was not significantly decreased during durability tests.
Therefore, results of this study supported the hypothesis that bond strength provided by one-bottle bonding agent to LDS deteriorated over time due to long-term immersion in water.Deterioration stemmed from inadequate chemical bonding, which in turn stemmed from the hydrolysis of MPTES within the product over time.

Applicability of Tokuyama Universal Bond II as a Pretreating Agent
In this study, when Tokuyama Universal Bond II was used with both adhesive and self-adhesive resin cements, good bond strength results with LDS were obtained [Tables 7 and 9a].In other words, a two-bottle bonding agent was useful in attaining durable bond strength between LDS and resin cement.
In addition to the effect of the new functional monomer, New 3D-SR monomer (Table 2), the bonding efficacy of Tokuyama Universal Bond II could be attributed to storage stability at room temperature and the improbability of MPTES hydrolysis and depletion in a two-bottle composition [14,20,22].
For intraoral applications, results of this study showed that Tokuyama Universal Bond II is a viable pretreatment substitute for HF.Beyond the present manufacturerrecommended use, its future application could be expanded to be a general-purpose pretreating agent for bonding between resin cements and LDS

Limitation
Limitations of the present study are inherent to the in vitro design, where only controlled variables were considered.Intraoral temperature changes might influence the long-term outcome of indirect restorations since the different materials employed in this study presented higher thermal contraction/expansion coefficients than teeth [14].

Conclusions
(i) With HF pretreatment, the shear bond strengths of each resin cement were not significantly different among the three time periods (after one-day water storage, TC 5k and TC 20k).Without HF pretreatment, Tokuyama Universal Bond II and Super-Bond Universal showed the highest values at TC 5k and TC 20k, which were significantly greater than the other resin cements.(ii) At TC 20k, Tokuyama Universal Bond II and Super-Bond Universal showed significantly better results than others when treated with the recommended bonding

2 .
Statistical Comparison within Each Time Period among Nine Resin Cements (Table

Figure 3 .Figure 4 .
Figure 3. Absorption wavelength of peak at retention time of 67.2 min for Tokuyama Universal Bond II

Figure 3 . 1 Figure 2 .
Figure 3. Absorption wavelength of peak at retention time of 67.2 min for Tokuyama Universal Bond II.

Figure 3 .Figure 4 .
Figure 3. Absorption wavelength of peak at retention time of 67.2 min for Tokuyama Universal Bond II

Figure 4 .
Figure 4. Absorption wavelength of peak at retention time of 67.2 min for MPTES.

Table 2
lists the manufacturer-recommended pretreating agents for the resin cements listed in Table

Table 2 .
Pretreating agents used in this study.

Table 3 .
Shear bond strengths between e.max and resin cements with and without HF pretreatment (MPa, mean (standard deviation), Adhesive failures).

Table 4 .
Comparison of the means (Tukey-HSD) of shear bond strengths of each resin cement among three time periods (groups with same superscript letters are not significantly different, p > 0.05).

Table 5 .
Comparison of the means (Tukey-HSD) of shear bond strengths at each time period among the nine resin cements (groups with same superscript letters are not significantly different, p > 0.05).

Table 6 .
Comparison of the means (t-test) of shear bond strengths between HF (+) and HF (−) specimens of each resin cement for each time period.

Table 10 .
Comparison of the means (t-Test) of shear bond strengths between two pretreating agents at Base and TC 20k respectively.